The invention relates to suspensions for vehicles for cushioning shocks on an axle assembly caused by irregularities in the track or ground before they can be transmitted to the vehicle frame.
Personnel, and some supplies, are transported about underground mines in battery- or trolley-powered personnel cars, sometimes called jeeps or portal buses, having flanged railway-type wheels running on mine track. Most mine track undulates because it is not economical to install it with above-ground precision or to prepare a deep, stable foundation for it. Once installed, the track condition worsens in use because of irregular heaving or swelling of the mine bottom, roof falls, and the constant back and forth shuttling of mine cars and locomotives. It is not unusual in a modern large mine for miners to be transported in personnel cars as much as three to five miles between the entry and their working places. This can require a ride of up to an hour at the beginning and end of the shift, during which time the miners are confined to the car, often in prone or crouched positions to clear the roof and supporting beams.
Up to a few years ago, miners were transported in empty mine cars or shuttle cars. Sometimes they walked, or even crawled part way. Use of mine cars, locomotives, and shuttle cars for this use diverted production machinery from its primary purpose; further, cars made for hauling and dumping coal and ore were not comfortable and sometimes not even safe. Occasionally, to go between working areas during a shift, a few miners would hitch a ride on the top of a locomotive or in a mine car. It has been only recently that special cars have been made primarily for transporting personnel. They have been manufactured primarily for safety with comfort features such as cushioning and roominess secondary. In some personnel cars, one or more axles are trunnion-mounted, rocking about longitudinal pivotal connections to the frame at the center of the car. This eliminates the requirement for journal boxes and allows the cars to adapt to varying track conditions and negotiate curves without derailment. It saves cost and in some cases lowers head room requirements. However, although the trunnion mount enables the axle assembly to rock about pivotal connections to accommodate up and down irregularities in the track or ground, the pivotal connections fore and aft of the axle housing have been solidly connected to the frame and transmitted shocks, uncushioned, directly from the axle assembly to the frame and to the miners riding inside. Even though some cushioning results from rocking the axle assembly upward against springs, this can be most uncomfortable on a long trip underground.
The early personnel cars were substantially improved by the development of a rocking hinge-type suspension. This was similar to the trunnion-mounted suspension described in the above paragraph except that one of the trunnion swivel blocks swung upwardly against springs. Two examples of this construction are shown in U.S. Pat. No. 4,085,682 issued Apr. 25, 1978 to Robert C. Nelson et al, and U.S. Pat. No. 4,213,399 issued July 22, 1980 to Eric DeBrick. These represented substantial improvements. They provided a relatively short up and down displacement of the vehicle frame for advantageous use in low headroom mines, yet provided double acting shock absorption, first by rocking the axle assembly about a longitudinal axis through trunnions as previously described and, in addition, tilting the axle assembly up and down about a hinged end. Springs absorbed shocks from both tilting and rocking movements. Rider comfort was improved, especially on long trips. However, these suspensions had some limitations which prevented them from fully exploiting the rocking hinge principle.
The suspension in U.S. Pat. No. 4,085,682 would not tilt up and down unless the axle was first moved to a nearly horizontal position. As a result, at any moment when the axle assembly was rocked out of a horizontal position, vertical tilting about the hinged end had to be preceded by rocking the axle assembly to or near a horizontal position. This created wear and communicated shock to the riders.
The suspension in U.S. Pat. No. 4,213,399 was developed primarily for locomotives. A special connecting means was provided between the vehicle frame and the axle assembly at the hinged end. This did not permit unrestricted sidewise swinging movement of the axle assembly to accommodate sidewise movement at the tiltable end in case excessive clearance existed there.
In both prior art constructions illustrated by the above-mentioned patents, the relatively movable parts at the hinged end must be made with substantially more clearance than is desirable to prevent binding and shock transmission to riders; if such excessive clearance were not provided when the vehicle was manufactured, the parts would wear that way in use.